The present invention relates generally to the field of devices for controlling the speed of rotating bodies. More particularly, the present invention concerns an apparatus for controlling the speed of an electrically driven momentum wheel in an inertial guidance system. Specifically, the invention is embodied in a closed loop speed control system capable of regulating speed to an accuracy of better than 0.0035%.
A great variety of electrical and electronic devices for controlling and regulating the speed of rotating mechanisms has evolved. Analog systems generating an electrical signal which has a magnitude proportional to the speed of the rotating body, comparing this signal with a reference signal, and employing a closed loop feedback control system to vary the speed of the rotating body to reduce the difference or error signal have been in existence from a time prior to solid state electronics.
More recently, with the advent of inexpensive integrated digital circuitry, a new generation of speed controllers has evolved. Typically, the sophistication and circuit complexity which can be simply realized with the use of such integrated digital components has made possible improvements in the accuracy and stability with which rotational speed can be regulated.
However, there remain applications for speed control mechanisms which set such high requirements for regulation accuracy as to challenge the existing regulator designs. One such application is in inertial guidance systems for satellite spacecraft, where a plurality of momentum wheels oriented along different axes of rotation are used to orient the spacecraft antenna system with a ground station antenna system to a very high degree of accuracy. In order to alter or correct the orientation of the spacecraft, the momentum wheels must be speeded up or slowed down, while to maintain a given orientation, these wheels must be maintained at a well-regulated controlled speed.